Silicon oxycarbide is an amorphous ceramic material with a structure deriving from silica (SiO2), in which bivalent oxygen atoms have been replaced by tetravalent carbon atoms.
Silicon oxycarbide in its glass or fiber form has better chemical, physical and mechanical properties than common silica glass or than silica-based glasses (such as soda-lime glass, borosilicate, aluminosilicate, etc.) and than silica glass fibers or silica-based glass fibers (such as soda-lime glass, borosilicate, aluminosilicate, etc.).
Silicon oxycarbide glasses and fibers are excellent for use in environments requiring high chemical resistance under strongly acid or basic pH conditions, resistance to devitrification and to decomposition in oxidizing or reducing atmospheres, high elastic modulus and high thermal stability.
A process for producing silicon oxycarbide glass was described in document IT-A-1,248,657 issued to General Electric Company. The method basically envisages pyrolysis at temperatures between 900 and 1600° C. in non-oxidizing atmosphere of previously reticulated methyl silicone resins. The methyl silicone resins used contain methyl groups bonded to silicon atoms and alternated bonds of silicon and oxygen atoms with a branched polymeric structure. The reticulation of these resins takes place by adding to a solution of said resin in a solvent, such as for instance toluene, a reticulating agent, such as gamma-aminopropyl-triethoxysilane. In particular, reticulation occurs when the hydroxyl units that are present in the resin combine so as to form a Si—O—Si bridge bond releasing water.
Known methods for producing silicon oxycarbide ceramic fibers starting from a silicone polymer comprise the following steps:                i) spinning of a composition comprising a silicone polymer and a reticulating agent;        ii) chemical reticulation of fibers obtained from step i);        iii) pyrolysis of reticulated fibers at a temperature of 800-1600° C. in non-oxidizing atmosphere.        
A process for producing silicon oxycarbide fibers according to the method mentioned above is described in patent U.S. Pat. No. 5,358,674 belonging to Dow Corning Corporation. Fibers are produced starting from a composition comprising a basically linear polysiloxane consisting of [R2SiO] units, in which R can be hydrogen or a saturated or unsaturated hydrocarbon radical, and a reticulating agent consisting of a photo-initiator. In this method it is essential that at least 20%, and preferably 50%, of said [R2SiO] units contains at least an unsaturated hydrocarbon R (for instance [MeViSiO], where Me refers to a methyl group and Vi to a vinyl group). The composition is spun and then fibers are reticulated by irradiation with UV rays which activate the photo-initiator. The fibers thus reticulated undergo pyrolysis at a temperature between 800 and 1000° C. in non-oxidizing atmosphere (vacuum, argon, etc.).
The aforesaid document mentions the presence of Si—H bonds in the starting polysiloxane (when R is a hydrogen atom); the solution referred to identifies as an essential element of the invention the presence for reticulation of unsaturated bonds in R substituents of [R2SiO] units constituting the polysiloxane, which bonds are activated by the photo-initiator.
These methods for producing silicon oxycarbide ceramic systems result in a product comprising a substantial portion of carbon atoms bonded to silicon atoms and a significant portion of carbon atoms as elementary carbon dispersed in the glass matrix.
There is therefore the need for technologies for producing silicon oxycarbide ceramic fibers, which are cheaper than known methods and can generate ceramic fibers with a given composition and structure, i.e. with quite a high number of carbon atoms having covalent bonds with silicon atoms, and with better mechanical, thermal and chemical properties than fibers obtained with production methods known in the field.
It has already been suggested to produce silicon oxycarbide ceramic fibers with better chemical properties than those known today, for instance with tensile strength up to 750 MPa and elastic modulus up to 125 GPa.